Diffusion and osmosis

Diagram Of Diffusion

2. Examples of diffusion
Have a look at these examples of a diffusion gradient.You need to learn at least one example.

Example
Particles continue to move from high to low concentration for as long as there is a concentration gradient.
For example, the blood constantly removes oxygen from alveolar air spaces in the lungs, provided that there is more oxygen in the alveolar air spaces than in the blood.
The circulation takes the oxygen-rich blood away and replaces it with blood low in oxygen.

Diagram of Example of Diffusion

3. Osmosis 

• Some membranes in plant and animal cells allow certain particles to pass through them and not others. They are selectively permeable.
  
• The diffusion of water through a selectively permeable membrane is called osmosis. The rate at which osmosis takes place is affected by the concentration of water in the two solutions on each side of the membrane.

• If a selectively permeable membrane separates the two solutions, water moves through it in both directions at the same time. However, more water leaves a dilute solution (high water concentration) and passes into a more concentrated solution (low water concentration) than enters it. Although the water appears to move across the membrane in one direction, it is in fact moving in both directions but more one way than the other.
  
• When the concentration of water is the same on both sides of the membrane, the movement of water will be the same in both directions. At this point, the net exchange of water is zero and the system is in equilibrium.

Diagrams Of Osmosis

Wise-up words

To help you remember these words write them down with their meanings on a card called 'Movement of particles'.